The present invention relates to probes, and more particularly, to a micro probe apparatus and probe assembly.
Probe technology is used in a wide variety of applications. Typically, in many situations it is necessary to establish an electrical connection to an electronic circuit wherein the contact is very small. Probes, sometimes referred to as “micro probes” are typically used to establish such connections. A common example of the use of probe technology is in the testing of integrated circuits. When an integrated circuit is manufactured, the many repetitions of the same circuit are commonly included as an array on a silicon wafer. It is generally desirable to test the circuits on the wafer before the wafer is cut and the individual circuits are packaged. Each circuit will typically include numerous contact pads. To test the circuits on the wafer, it is necessary to establish a connection between electronic test equipment and the contact pads for each circuit on the wafer. Probe technology is commonly used to establish such connections.
FIGS. 1-3 illustrate a prior art probe test head for vertical probe technology. In vertical probe technology, the probes stand up vertically over the contact site, rather than approaching the contact site at an angle. The probe head consists of an array of probes between and upper die 42 and lower die 44. The upper and lower dies 42, 44 contain patterns of holes corresponding to spacing on an integrated circuit contact pad spacing which forms a lower die hole pattern and upper die hole pattern. The upper end of each of the probes is retained by the upper die hole pattern, and the lower end of each of the probes passes through the lower die hole pattern and extends beyond the lower die 44 to terminate in a probe tip. As illustrated in FIGS. 2 and 3, the lower die holes are offset from the upper die holes, and the offset is formed into each probe 101 such that the probe acts like a spring.
FIG. 4 illustrates the use of prior art vertical probes to contact solder bump arrays. Vertical probe cards, which are sometimes referred to as “buckling beam” probes, are used for testing semiconductor applications such as microprocessors, DSP's, and other advanced logic/ASIC devices that include bump arrays used as contacts for wafers in flip-chip applications (e.g., flip chips). When the test head is brought into contact with a bump 401, the upper end of the probe remains predominately stationary, while the lower end compresses into the body of the test head. One important parameter limiting the use of vertical probes is the distance between the contacts, which here is the pitch, “p”, between bumps. As the contacts move closer together, or as the bumps become smaller, it becomes necessary to decrease the distance between adjacent probes. However, as described below, existing probe technologies have limitations impeding the ability to reduce such dimensions.
Another problem with existing probe technologies pertains to the assembly and repair of the probes. During assembly, each probe must be inserted into a hole in the upper and lower dies. However, some precaution must be taken to secure the probe in place. For example, if probe 101 in FIG. 3 is not secured in some manner, it may fall through the hole in the lower die. Additionally, any securing mechanism must account for the necessity of removing and replacing damaged probes. For example, it is generally undesirable to weld or solder the probes in place because such a securing technique may make removal and replacement of damaged probes unduly burdensome, time consuming, and costly.
FIGS. 5A-B illustrate one prior art probe. Probe 5000 is referred to herein as a flattened swaged probe. FIG. 5A shows one view of the probe to illustrate a prior art technique for securing the probe in a probe assembly. The probe includes a flattened swaged intermediate region 5003 (e.g., stamped) between an upper end 5001 and lower end 5005. The probe is typically formed by swaging or stamping a straight wire to produce the desired probe shape and thickness. This swaging process flattens and widens the center, curved portion of the probe in order to achieve a desired force per mil of probe deflection. As illustrated in FIG. 5B, the flattened swaged region causes the probe to have two diameters. The lower contact end has a first diameter d1, and the flattened swaged region has a diameter d2. Accordingly, when the lower contact end is inserted into a hole of a lower die, the protruding structure created by the flattened swage and having a larger diameter will create a probe stop to set the distance the probe will extend below the lower surface of the lower die and stopping the probe from sliding through the hole. However, flattened swaged probes may reduce the current handling ability of the probe in the area between the flattened region and each contact end.
FIG. 6 illustrates another prior art probe design. Probe 600 is referred to herein as a tapered probe. Tapered probe 600 include two regions of different diameters. The lower contact end of the probe to be inserted into a hole of a lower die may have a narrower diameter “d1” than an intermediate region of the probe that has a wider diameter “d2”. The tapered region 601 between the lower contact end of the probe and the intermediate region of the probe ensures that the probe is secure in the assembly. The tapered region ensures that the probe does not slide through the hole in the lower die during operation. However, similar to the flattened swaged probe described above, the protruding material created by the taper impacts the spacing required between the holes of the lower die.
FIG. 7 illustrates a prior art protruding notch probe design. In this probe design, a protruding notch 701 between the lower contact end of the probe and the intermediate region extends out above or beyond a surface of the hole in the lower die thereby securing the probe. However, similar to the shortcomings of the probe designs described above, the protruding material created by the protruding notch impacts the spacing required between the holes of the lower die. Moreover, the prior art techniques for securing the probes described above can be complicated or inefficient to manufacture.
FIG. 8 illustrates another prior art probe assembly. In this example, a membrane 1301 is provided at the upper contact ends of the probes below the upper die. Such membranes are typically permanently attached by a bond. Another aspect of the present invention includes probes and assemblies that improve both the ability to replace damaged probes and repair probe assemblies and the reliability of the contacting vertical motion of the probes.
The present invention solves these and other problems with an improved probe and probe test head assembly.